False-twist texturing process with improved feed yarns and feed rates

ABSTRACT

Improvements in a conventional false-twist texturing process are disclosed which produce textured polyester yarn of improved quality (compared with that produced by conventional false-twist texturing) of the type obtained by known draw-texturing processes without the unstable feed yarn problems and feed yarn rupturing at start-up (and hence apparatus modification) problems incident thereto. The improvements comprise utilizing as the feed yarn in a conventional false-twist texturing process, a polyester yarn having (1) a spin-drawn orientation, free of mechanically-drawn orientation, with a birefringence within a range of the order of 0.02 to 012, (2) a percentage elongation-to-break within a range of the order of 60% to 200%, and (3) a zero-strength temperatue above approximately 235*C; and continuously positively feeding the feed yarn into and out of the texturing zone provided by the apparatus in performing the process, while maintaining the twistsetting temperature or heater temperature of the apparatus below the zero-stength temperature of the feed yarn, at feed rates into and out of the texturing zone in accordance with the formula DR &gt; (OR) (EB/100 + 1)) wherein DR is the feed rate of the feed yarn out of the texturing zone divided by the feed rate into the texturing zone, or is a constant within a range of the order of 0.63 to 0.70, and EB is percentage elongation-to-break of the feed yarn.

United States Patent [191 Small 1 June 18, 1974 [54] FALSE-TWIST TEXTURING PROCESS wirn IMPROVED FEED YARNS AND FEED RATES [75] Inventor: Ronald J. Small, Greensboro,'N.C.

[73] Assignee: Burlington Industries, Inc.,

Greensboro, NC.

22 Filed: Apr.l1,1973 21 App]. No: 349,930

3,747,318 7/1973 Cochrane 57/157 TS Primary Eraminer-John Petrakes Attorney, Agent, or Firm-Cushman, Darby & Cushman l 5 7 ABSTRACT Improvements in a conventional false-twist texturing process are disclosed which produce textured polyester yarn of improved quality (compared with that pro duced by conventional-false-twist texturing) of the type obtained by known draw-texturing processes without the unstable feed yarn problems and feed yarn rupturing at start-up (and hence apparatus modification) problems incident thereto The improvements comprise utilizing as the feed yarn in a conventional false-twist texturing process, a polyester yarn having (1) a spin-drawn orientation, free of mechanicallydrawn orientation, with a birefringence within a range of the order of 0.02 to 012, (2) a percentage elongation-to-break within a range of the order of 60% to 200%, and (3) a zero-strength temperatue above approximately 235C; and continuously positively feeding the feed yarn into and out of the texturing zone provided by the apparatus in performing the process, while maintaining the twist-setting temperature or heater temperature of the apparatus below the zerostength temperature of the feed yarn, at feed rates into and out of the texturing zone in accordance with the formula DR (OR) [EB/100 1)]wherein DR is the feed rate of the feed yarn out of the texturing zone divided by the feed rate into the texturing zone, or is a constant within a range of the order of 0.63 to 0.70, and EB is percentage elongation-to-break of the feed yarn.

4 Claims, 2 Drawing Figures F ALSE-TWIST TEXTURING PROCESS WITH IMPRQVED FEED YARNS AND FEED RATES This invention relates to false-twist texturing of multifilament polyester yarns and more particularly to im provements in the process of producing false-twist textured yarns.

The popularity and use of textured multifilament polyester yarns has continued to increase within the past several years. While a number of different processes and machines have been developed and used to produce textured polyester, probably the most widely used process is the well known falseat'wisting method. This method consists essentially of continuously passing a fully drawn feed yarn into and out of a texturing zone, maintaining a false twist in the feed yarn within the texturing zone by continuously. imparting a twist to the yarn at a twisting position spaced downstream from an upstream position of restraint, and raising and then lowering the temperature of the yarn during the continuous movement thereof between the upstream position of restraint and the twisting position to heat-set the twist therein. i

It hasbeen known throughout the recent expansion of the practice of false-twist texturing that the conventional false-twist texturing process could be combined with the conventional drawing process performed by producers. The knownprocedures for combining drawing and false-twist texturing include both sequential and concurrent performance of the two processes. Sequential performance involves the utilization of conventional drawing equipment in series upstream for the false-twist texturing equipment so that the undrawn feed yarn is first drawn and then false-twist textured, both at compatible speeds. The sequential performance of drawing and false-twist texturing, effectively in two zones on the same machine, produces yarn which is comparable to conventionally pre-drawn textured yarn. From an overall process standpoint, the sequentially combined procedures decrease the yarn handling required in comparison with conventional procedures. On the other hand, the efficiency of the conventional drawing procedure is reduced when sequentially combined with false-twist texturing due to the lower speeds at which the drawing must beperformed to make it compatible with the falsetwist texturing.

Concurrently combined drawing and false-twist texturing involves drawing the yarn essentially simultaneously with false-twisting. The equipment utilized thus provides but one treatment zone as distinguished from the two treatement zones of the sequential procedure), in which single zone the undrawn feed yarn is both drawn and false-twist textured. In one proposal of a concurrent or one-zone process disclosed in the patent literature (British Patent No. 1 ,263,055), the improved dyeing uniformity of the resultant product, compared with similar yarn produced from previously fully drawn yarn, is attributed to the lower rate at which drawing takes place and to the concomitant increased time for heating the yarn. From an overall process standpoint, the same advantage of a decrease in yarn handling is obtained compared with the conventional separate drawing and texturing. However, a severe operating difficulty is introduced'which is not present in either conventional false-twist texturing or two-zone draw texturing. This difficulty is that of undrawn feed yarn rupturing in start-up.

The problem of feed yarn rupture in start-up is dealt with at length in the aforesaid patent. As stated therein, conventional undrawn polyester feed yarns will yield and rupture too readily under tension if heated too soon at higher temperatures than their second-order transition temperature of about 90l00C, which higher temperatures are in the range normally present in the heater. Consequently, means are provided for maintaining the undrawn polyester feed yarn closely adjacent to but out of contact with the heater at startup until drawing is observed, at which time transfer of the feed yarn into contact with the heater can be effected. The necessity to prevent undrawn feed yarn breakingat start-up effectively prevents the utilization of all conventional false-twisting equipment utilizing enclosed contact heaters and requires severe modification of open-faced contact heater equipment.

From another viewpoint the aforesaid problem of yarn breaking in start-up may be said to arise from the fact that the feed yarn of British Patent 1,263,055 is a relatively low-melting conventional as-spun polyester, subject to ready sticking to hot surfaces and to loss of strength in'the region of 90l0 0C. The patent reveals that itsfeed yarns are subject to drawing atdifferent draw ratios, between 2.9 and'3.65 the standard draw ratio for this yarn). Elsewhere the art shows that such yarns have maximum draw ratios of 6-7: 1, but that the draw ratios actually used in production are in the more practical range of 3:1 to 5:] (cf. I. Goodman and J. A. Rhys, Polyesters, Vol. 1, page 50, lliffe Books Ltd., 1965). These art yarns clearly are of a different kind from the high zero-strength temperature, highly spinoriented feed yarns of the present invention. These latter yarns have a maximum elongation-to-break of the order of 200 percent, i.e., a maximum draw-ratio of 3.0. Actually, within the teachings of the invention they are textured at maximum draw-ratios of not more than 2.1, i.e., 70% of 3.0, and preferably lower than 2. 1.

Furthermore, despite all of the knowledge which has been developed with respect to combining the drawing and false-twist texturing processes, the-relative advantages of the combination have been secured only by those small segments of the texturing industry which have integrated their operations to include spinning, drawing, and false-twist texturing. The major segment of the industry is made up of throwsters whose historical practice has been to obtain drawn yarn from producers as feed yarn for their processes. Such throwsters are reluctant to .take the risks inherent in obtaining undrawn yarn from producers because of the amorphous nature of such yarn and the known ageing problems inherent therein. Prolonged storage of these yarns causes severe deterioration of the properties thereof to the point where further processing is nearly impossible.

Use of undrawn yarns commercially by throwsters would require strict inventory control and a first in/first out processing sequence.

It is an object of the present invention to provide an improved method of false-twist texturing multifilament polyester yarns which obtains all of the advantages of known combined drawing and false-twist texturing processes while eliminating the disadvantages thereof, thus making it possible for throwsters to produce better yarn than currently produced by conventional processes, with the use of all existing equipment without serious modification, such as that required to prevent yarn melting on start-up, from feed yarn obtained from producers which does not present an ageing, sticking, or other production or storage problem.

In accordance with the principles of the present invention, this objective is obtained by utilizing as the feed yarn in a conventional false-twist texturing process, a polyester yarn having l a spin-drawn orientation, free of mechanically-drawn orientation, with a birefringence within a range of the order of 0.02 to 0.12, (2) a percentage elongation-to-break within a range of the order of 60% to 200%, and (3 )'a zero-strength temperature above approximately 235C; and continuously positively feeding the feed yarn into and out of the texturing zone provided by the apparatus in performing the process, while maintaining the twist-setting temperature or heater temperature of the apparatus below the zero-strength temperature of the feed yarn, at feed rates into and out of the texturing zone in accordance with the formula DR (OR) HEB/100 1 wherein DR is the feed rate of the feed yarn out of the texturing zone divided by the feed rate into the texturing zone, OR is a constant within a range of the order of 0.63 to 0.70, and EB is the percentage elongation-tobreak of the feed yarn.

By utilizing a feed yarn of the type specified above, the risk and problems incident to the instability and unoriented nature of undrawn polyester yarn are substantially eliminated since yarn of the type specified has a stability against ageing essentially equal to drawn yarn. Moreover, by maintaining process limitations as to heat-setting temperatures and feed rates in the manner specified while processing such feed yarns, the problem heretofore encountered with respect to feed yarn rupturing at start-up is elminated since the heating temperature of the process is maintained below the zerostrength point of the feed yarn. Moreover, by following these process procedures the product which is obtained thereby secures all and more of the uniform dyeability advantages attributable to the processing in accordance with the aforesaid patent. Thus, notonly is a conventional throwster enabled to produce improved textured yarn, but such production can be obtained without the risk or problems incident to the unoriented nature of undrawn yarn, and the throwster is able to secure all of these advantages by the use of existing equipment simply by using the correct feed yarn and varying the feed rates into and out of the texturing zone. Furthermore, since the formula noted above bears a direct relationship to yarn denier, a throwster practicing the principles of the present invention is enabled to clearly specify to the yarn producer the essential characteristics of the feed yarn necessary in order to produce the textured yarn desired by the throwster.

The aforesaid objective as well as other objects of the present invention will become more apparent during the course of the following detailed description and appended claims. 1 1

The invention may best be understood with reference to the accompanying drawings, wherein an illustrative embodiment is shown.

In the drawings:

F IG. 1 is a schematic view of one embodiment of an apparatus for carrying out the process in accordance with the principles of the present invention; and

FIG. 2 is a somewhat schematic view of a yarn test frame utilized in the measurement of feed yarn elongation.

Referring now more particularly to FIG. 1, there is schematically illustrated therein a single-zone type of false-twist texturing apparatus including the usual conventional components, each of which may be of any conventional construction. As shown, a supply of highly spin-oriented polyester feed yarn in the form of a yarn package 10 is provided in accordance with the principles of the present invention, from which package feed yarn 12 is drawn, as by a feed-roll mechanism 14 or the like. The feed-roll mechanism 14 serves to continuously feed the yarn 12 into a texturing zone, indicated at 16, from which the yarn is continuously drawn by a draw-roll mechanism 18. The yarn 12 passing through the texturing zone 16 moves past a falsetwisting device, schematically indicated at 20, at a position intermediate the ends of said texturing zone, so as to impart and maintain in the feed yarn 12 a twist in one direction which extends upstream to the feed-roll mechanism 14. The twist imparted to the portion of the yarn 12 passing between the feed-roll mechanism 14 and the false-twisting device 20 is heat-set by elevating and lowering the yarn temperature by a heater generally indicated at 22. The heater, as shown, is of the enclosed type, but it will be understood that open-faced contact type heaters, as well as other types, may be used. The above-identified process and apparatus for texturing polyester yarn by heat-setting a false twist therein are conventional as aforesaid-Likewise, in accordance with conventional practice, the yarn 12 passing from the draw-roll mechanism 18 out of the texturing Zone is then wound up in a package. Other treatments may be applied either before wind-up or after, depending upon the torque, stretch, set, and other characteristics desired in the finished textured yarn.

The present invention is more particularly concerned with improvements in this conventional procedure relating to the feed yarn l2 utilized and certain temperature and feed rate conditions utilized in conjunction with the particular feed yarn to achieve the objectives of the present invention. A basic essential of the feed yarn utilized in accordance with the principles of the present invention is that the yarn must be of the drawspun highly spin-oriented type free of mechanicallydrawn orientation, except insofar as spin-orientation, implemented by fast-turning take-up rolls, is itself a form of mechanical orientation. What is meant to be excluded are such roller or the like induced, postspinning orientation processes as cold or hot drawing, as these terms are commonly accepted in the fiber drawing art, whether mechanical means or their manual equivalents are used. Generally, but not necessarily, so-called necking-down" is a part of the orienting processes to be avoided.

It should be noted that the designation of feed yarns as being free of mechanically-drawn orientation refers not only to avoidance of yarns conventionally drawn in a wholly separate step after spinning, but also of any other drawing which may be applied to the solidified feed yarn prior to its entry into the texturing zone, i.e., zone 16 of FlG. 1. Applicant has found that the advantages of the invention cannot be achieved with yarn subjected to the aforesaid mechanical orientation before introduction into the process of the invention.

Spin-drawn yarn is known in the art and is produced by pulling the same from the spinneret during spinning at a substantially greater rate than is utilized in the production of conventional undrawn yarn. Spin-drawn yarn of this type. utilized in accordance with the principles of the present invention may require spinning wind-up speeds as high as of the order of 3,000 to 4,000 meters per minute. The theoretical aspects of spindrawing and the differences between spin-drawn and conventionally drawn yarn are discussed in articles by A. Ziabicki and K. Redzierska in the Journal of Applied Polymer Science, Volume IN .1959), pages 14-23, and Volume VI (1962), pages 1ll-l l9 and 36l-367, which are hereby incorporated by reference herein. Typical preparations of spin-oriented yarns are described in US. Pat.'Nos. 3,513,110 and 3,551,363.

As to the extent of orientation imparted to the feed yarn during the draw-spinning procedure, perhaps the most direct measure of orientation is the birefringence of the yarn. The present invention contemplates a partial orientation in which the birefringence is within a range of the order of 0.02 to 0.12. The birefringence values thus occupy a zone intermediate to the nearzero readings of conventional producer-spun polyester and the 0.14 to 0.18 and higher birefringence of lowto high-tenacity drawn polyester yarns. Essentially duplicate birefringence measurements have been made on yarns of the invention by the flat wedge method of R. G. Quynn and R. Steele (Textile Research Journal, 23, 258-9 1953)) and by a compensator method (see discussion of latter methods in H. J. Woods, Physics of Fibers, Reinhold Publishing Corp., 1955, pages 50-4).

Its elongation-to-break, which in accordance with the present invention lies within a range of the order of 60% to 200%, is an important property of the feed yarn used. Like the birefringence, the elongation (used herein as synonymous with elongation-to-break) is intermediate in'value between the high (about 600%) elongation of producer-spun and the low (40%) elongation of conventional pre-drawn feed yarns. The elongation, together with the accompanying high zerostrength temperature, more than any other property determines the processability of the feed yarn and the resulting superior properties of the final draw-textured yarn. The elongation is read at the point of maximum lnstron loading.

Currently'commercial spin-drawing technology appears capable of producing a polyester feed yarn whose practical minimal elongationto-break is of the order of 100%. At the upper end of the elongation range, the

higher the elongation of thefeed yarn, the greater the risk of start-up difficulties arising from a zero-strength temperature of marginal sufficiency. In the light of these facts an elongation range of 100-160% is generally preferred for practicing this invention.

An accurate and reproducible measurement of the feed yarn elongation is essential to successful utilization of the process of the invention, yarn slippage due to neckdown in the lnstron jaws being a particularly serious source of error. This problem may be avoided by use of the yarn test frame depicted in F l6. 2. The frame comprises a cardboard 30 with a rectangular hole having a width of 5.0 inches and a length of about 7-11 inches, across which hole are laid yarn samples 31, ee-

mented to the cardboard with smoothed spots of Duco cement 32 at about l-inch intervals. lndividually cardtabbed yarn samples are removed by cutting along lines 33 after at least two hours of drying, and the tabs are clamped in the lnstron jaws at yarn pretension of 0.1 g/d. Extension rate is 200% per minute, and results of 6 at least five breaks are averaged for each reading. Elongation is read from the point of initial load to the point of total rupture.

The foregoing considerations take into account the importance of the yarn having a high zero-strength temperature, defined as the lowest temperature at which the yarn breaks quickly when contacted with a hot surface while under a light load. As discussed hereinbefore, the start-up of the drawtexturing process when using conventional, unoriented, producer-spun yarn must be effected under carefiully controlled conditions because of the lowbreaking temperature of the yarn. One of these conditions is that only an open-faced contact-type texturing heater may be used, with the yarn being held away from the heater until drawing commences, as described in the aforementioned British patent. Practically speaking, a closed heater at operating temperature cannot be used at all with unoriented yarn. Feed yarns of the present invention, on the other hand, having zero-strength temperatures of at least approximately 235C, may be textured on any conventional false-twisting apparatus without special start-up precautions. Since 235C .is above the conventional temperatures normally employed in false-twist texturing of polyester, the 235C zero-strength minimum temperature required of the feed yarn affords ample protection so long as the heater temperature is held under reasonable control.

The zero-strength temperature is conveniently determined on a conventional Parr or Dennis gradient-bar melting point apparatus. The yarn specimen, loaded at its free-swinging lower end with a brass weight of 0.07 g/d, is draped across the bar at spots progressively closer to its hot end until the point of essentially instantaneous yarn breakage isreached. A fresh yarn sample is used for each contact with the bar.

The success of the present invention dependsnot only upon the properties of spin-drawn polyester feed yarns, as expressed by their hereinbefore discussed birefringence, elongation-to-break range, and zerostrength temperature, but more particularly upon a highly useful and unexpected mathematical relationship discovered to exist between said elongation-tobreak (within the claimed range) and the rate of yarn drawn into and out of the draw-texturing zone of FIG. 1 during draw-texturing. This relationship may be expressed by the equation DR= (OR) [(EB/lOO) 1] (A) where DR is the draw-ratio or draft of the yarnduring draw-texturing, i.e., the ratio of the linear speed of the textured yarn leaving the texturing zone divided by the linear speed of spun-drawn feed yarn into'said zone; EB is the percentage elongation-to-break of said feed yarn; and OR is the orientation ratio, a factor or constant having a value within a range of the order of 0.63 to 0.70 and preferably, for the optimum balance of operating conditions and final textured yarn and fabric properties, about 0.66 to 0.67.

The OR factor itself is the ratio of the draft in drawtexturing to the draft-to-break of the spin-drawn feed yarn, or

OR draft in draw-texturing/draft-to-break of feed yarn i (B) elongation-to- Substitution of equation (C) into equation (B) and rearrangement produce equation (A), from which latter equation, given the elongation of a spin-drawn polyester feed yarn, one may calculate the best draw-ratio to apply in draw-texturing said yarn.

Ultimately the significance of equation (A) arises from the experimental evidence that over a wide range of elongation values for spin-drawn polyester yarns, the value of OR holds constant at about 0.66-0.67 for the best balance of textured yarn properties. The OR value may, however, range from about 0.63 to 0.70 without upsetting the balance, the precise number chosen being dependent upon the particular properties desired. On the other hand, conventional textured yarns are made under conditions of overfeed which, in the light of the elongations-to-break of their pre-drawn feed yarns, correspond to calculated OR values of the order of 0.75-0.78.

Drafts in both texturing and elongating to break are reciprocally related to the corresponding deniers; i.e.,

draft in draw-texturing feed yarn denier/drawtextured yarn denier, and draft-to-break of feed yarn feed yarn denier/feed yarn denier at break.

Substituting both of these equations in equation (B) produces the following equation for OR in denier terms: OR feed yarn denier at break/draw-textured yarn denier (D) The draw-textured yarn denier, as will be obvious to one of ordinary skill, refers to the denier of the yarn only within texturing zone 16, between the draw and feed rolls, and excludes the effects of overfeed and shrinkage after the draw-roll is passed. Said drawtextured denier is thus substantially analogous to the denier of the feed yarn in conventional texturing, which typically is smaller than the denier after heat-setting and packaging. Changes in a ISO-denier feed yarn to about l60-denier on the package are commonly observed.

Equation D) permits the easy calculation of the denier-at-break required in a spun-drawn feed yarn in order to yield any specified draw-textured yarn denier, at whatever value of OR is preferred, within the 0.63-0.70 range specified herein. By subsituting equation D) into equations (A) and (B), one may establish other relationships among denier, elongation-to-break, and draw-texturing draft, as will be apparent to one of ordinary skill.

For example, assume that a throwster desires to produce a l-denier (before heat-setting) draw-textured yarn. Substituting this value in equation (D) and assuming an optimum OR of 0.67, he first calculates that the spun-drawn feed yarn should have a denier-atbreak of 93.8. Then, based on the fact that the ratio of the feed yarn denier to the denier-at-break equals the draft-at-break, which by definition equals EB/ 100 l,

or feed yarn denier/denier at break draft at break elongation-to-break/ 1, he rearranges the first and last terms and thereby derives the equation (feed yarn denier X l00)/(denier at break) 100 elong'ation-to-break (E) By substituting the aforesaid 93.8 denier-at-break and a variety of proposed feed yarn deniers into equation (E), he readily calculates the corresponding elongations; for example, 200 denier-113% elongation, 220 denier-% elongation, and 250 denier-167% elongation. The fiber producer, in turn, principally by varying the rate of take-up of his yarn during draw-spinning, utilizing commonly known principles and skills of the art, can prepare any of these typical feed yarn denier- /elongation combinations. The preference will be that combination which offers optimum operating and ultimately economic advantages to both producer and throwster.

From the foregoing discussion it is obvious that higher and higher feed yarn deniers could be proposed for coupling with higher and higher elongations while still arriving at the same feed yarn denier-at-break. However, as indicated hereinbefore, above an elongation of about 200% it has been found that the orientation of the yarn becomes too low to maintain the high zero-strength temperature, with corresponding loss of most of the advantages of the invention. This fact thus has the effect of setting an upper limit on feed yarn deniers to be considered for conversion to prescribed draw-textured deniers. At the other end of the range of feed yarn deniers, where the elongations are becoming smaller, it has already been noted that present technology of spin-drawing limits the practically available elongation-to-break to a minimum of about 100%.

The special distinction of the limited range of numerical values designated herein for the OR factor, i.e., 0.63-0.70, is that both the range and particularly the preferred values, 0.66-0.67, are exceptionally low, compared to those calculated for conventional texturing. Their practical merit lies in the fact that they produce an unusually favorable combination of desirable yarn properties.

The invention may be utilized equally well with either singleor double-heater texturing machines. The second or heat-setting heater is outside the scope of the invention and its use is optional.

The invention is principally directed toward texturing the conventional polyethylene terephthalate type of polyester, but it may also be used effectively with other polyesters such as poly(cyclohexane-l,4-dimethylene terephthalate), poly(ethyleneoxybenzoate), and the like.

in runs typical of the process of the invention samples of spin-drawn polyethylene terephthalate feed yarn having a denier of 267.6, elongation of 127.6%, and tenacity of 2.13 g/den were single-zone draw-textured on an ARCT Model PTF-L 440-B texturing machine. The spindle speed was 331,060 rpm, and the enclosed double heaters were set at identical temperatures at successive 10C intervals from 180 to 220C. Orientation ratios were set at 0.78 and 0.67 (for -denier and denier draw-textured final yarns, respectively). Use of the 0.78 orientation ratio required a 1.784 draw ratio and of the 0.67 orientation ratio, a 1.528 draw ratio. A 62-tpi level of twist, based on the draw-roll speed, was inserted into the 0.78 orientation ratio samples, while above the spindle. At 067 OR they were about 27g below and 53g above. Normal tensions when texturing conventional ISO-denier polyester yarn are about 16-2lg below and 40-50g above the spindle, depending mainly upon the overfeed and twist levels used. Hence the tensions prevailing within the limits of the invention are near those which the throwster normally encounters. Excessive tensions are generally recognized to be harmful in terms of producing broken filaments and yarns, excessive machine wear, yarn slippage, buildup of finish on the guides, etc.

Recognition of the merits of the 0.63-0.70 OR limits, and preference for an OR of 0.66-0.67 for producing the best balance of favorable operating conditions and fiber properties, resulted from a series of such runs in the 0.63-0.78 OR range. Particularly desirable in the product yarns is a low level of thermally-induced dyedepth variation when they are textured at heater temperatures varied within the conventional 200 i20C range. It is well known that a primary source of dyedepth variation in conventionally textured yarns, and a principal cause of the fabric defect known as barre, is the occurrence of temperature differences in the heaters during texturing. Reduced sensitivity to such variations is highly advantageous. v The reduced sensitivity was observed by dyeing knit sample sleeves made from yarns which had been drawtextured at different temperatures. The yarns were knit as adjacent panels on a Lawson FAK circular knitting machine. After scouring, the sleeves were atmospherically dyed-together in a common bathusing 4 g/l of Liquid Carolid NLG (a 50%, anionic, self-emulsified, modified phenolic carrier made by Tanatex Chemical Corp.) and 1.5% of Latyl Blue FLW (a DuPont dispersed dye sensitive to potential barre), for 2 hours at the boil. (Similar samples dyed in separate compartments of an AHIBA sample dye machine gave similar results to those here.) The percent reflectance R of each panel was measured on a Kollmorgen KCS-l8 spectrophotometer and recorded at 620 nm, the point of maximum absorption. This reading was then converted to a K/S value of dye depth, where K/S equals l Ri /2R and increases with darker dye shades.

As a comparison of the dye depths of fabrics from yarn samples draw-textured over a range of heater temperatures, the K/S values of the 210C samples at each OR setting were designated as 100% dye depth, and each of these values was divided into the K/S values of the other samples draw-textured at that OR. At each OR setting, each sample lighter than the 210 sample had a percent dye depth lower than 100%, and each darker sample had a dye depth greater than 100%. Comparison of results from a large number of such runs established the fact that a lower OR produced significantly less dye depth variation than a higher OR. This was true when the high OR was associated with either draw-texturing or conventional texturing. The instrumental values may be viewed againstthe background fact that about one dye depth percentage unit in the 10 cited range is the minimum barely detectable by the average eye.

With respect to other quality characteristics of the yarn produced, crimp development in the present yarn was superior to that of conventional yarn. As to crimp stability, the elongation level to which crimp was stable was equal to or greater than that of conventional yarn. The load to which the crimpwas stable was, however, somewhat lower than with conventional yarns, but since it wasover 3 grams per denier, it was still quite satisfactory. The reason that the property of crimp stability is somewhat misleading is that, unlike with conventional yarns, it is possible to pull the crimp out of the yarns produced by the present invention before breaking filaments. This is due to the yarns higher than usual elongation level. Actually, this is of no consequence as long as the yarn is not subjected to tensions in excess of 3 grams per denier. Such excessive tensions would not normally be present during processing or use. The present yarn showed improved recovery properties in termsof percent tensile form recovery and of work to recover after five cyclic extensions to either 2% or 5% as compared with conventionally textured yarns. The present yarn dyes toa deeper shade and has less torque than conventional yarn but these properties may be at least partially attributable to the greater denier. The comparisons with conventional textured yarns apply equally well to high OR draw-textured yarns.

It thus will be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregiong preferredspecific embodiment has been shown and described for the purpose of illustrating the functional and structural principles of this invention and is subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.

What is claimed is:

1. In a process of texturing polyester yarn which includes the steps of continuously feeding yarn into and out of a texturing zone, maintaining a false twist in the yarn within said texturing zone by continuously imparting a twist to the yarn at a twisting position spaced downstream from an upstream position of restraint,

and raising and then lowering the temperature of the yarn during the continuous movement thereof between said upstream position of restraint and said twisting position to heat-set the twist therein, the improvement which comprises utilizing as the feed yarn in said process a yarn having l a draw-spun spin orientation free of mechanically-drawn orientation with a birefringence within a range of the order of 0.02 to 0.12, (2) a percentage elongation-to-break within a range of the order of 60% to 200%, and (3) a zero-strength temperature above approximately 235C, and continuously positively feeding said feed yarn into and out of said texturing zone, while maintaining said raised temperature below the zero-strength temperature of the feed yarn, at feed rates into and out of said texturing zone in accordance with the formula DR==(OR) [(EB/IOO) 1] wherein DR is the feed rate of the feed yarn out of the texturing zone divided by the feed rate into the texturing zone, OR is a constant within a range of the order of 0.63 to 0.70, and EB is the percentage elongation-tobreak of said feed yarn.

3,816,994 l 1 l2 2. The improvement as defined in claim 1 wherein 4. The improvement as defined in claim 1 wherein the percentage elongation-to-break of said feed yarn is said feed yam has a percentage elongation to break of 3. The improvement as defined in claim 1 wherein 100% to 160% and an OR of to OR isO.66toO.67. 5 

2. The improvement as defined in claim 1 wherein the percentage elongation-to-break of said feed yarn is 100% to 160%.
 3. The improvement as defined in claim 1 wherein OR is 0.66 to 0.67.
 4. The improvement as defined in claim 1 wherein said feed yarn has a percentage elongation-to-break of 100% to 160% and an OR of 0.66 to 0.67. 